Not sure if your point holds if you read more of the article, which implies that plenty of economists are critical of wage and wealth disparities just for different reasons. My personal read is that Piketty doesn't bother to come up with a "microfounded" rational for his theory and since this is the bread and butter of macro, his r > g theory hasn't been taken seriously. I will say that the basic empirical work of measuring the increase in inequality over the last fifty years seems to be taken very seriously. At least in my limited view of the discipline.